Solvent effects on mobile phases used in liquid chromatography: factor analysis applied to protonation equilibria and solvatochromic parameters

Dissociation constant values of the acid components of the standard NIST sc ale buffer solutions and of acetate buffer in several hgrdroorganic mixture s (acetonitrile-water, tetrakrydrofuran-water and methanol-water) were firs t subjected to factor analysis in order to obtain the number of factors tha t affect the variation of the whole data sets, and then to target factor an alysis to identify these factors. The pK(a) values were correlated with the Kamlet and Taft solvatochromic parameters (alpha, beta and pi*) of the sol vent mixtures according to the results obtained with these chemometric tech niques. Two or three factors emerged, depending on the range of percentage of organic cosolvent in the mixture, Target factor analysis results showed that Kamlet-Taft equations were reduced in these mixtures: the independent term and pi* solvatochromic parameter of porarity-polarizability appear up to 50% w/w of organic solvent, as does the hydrogen bond basicity beta solv atochromic parameter when data up to 70% w/w were analysed, Further, the qu asilattice quasi-chemical theory has been applied to quantify the preferent ial solvation by water of electrolytes in acetonitrile-water, tetrahydrofur an-water and methanol-water mixtures. An overview of the effect of this pre ferential solvation on the values of the protonation constants in these med ia was also obtained. (C) 1999 Elsevier Science B.V. All rights reserved.